Antenna system



Nov. 6, 1951 v. D. LANDON 2,573,914

ANTENNA SYSTEM Filed July 30, 1949 .ll. m. a U- .r I. N.... v

Z; I], INVENTOR l ermnfllmdwz ATTORNEY Patented Nov. 6, 1951 ANTENNA SYSTEM VernonD..Landon, Princeton,;N; J-., assignor-to Radio Corporation of America, .a corporation of.-

Delaware.

Applicatir1-Jlily -30, 1949; SrialNo. 107,792

81Claims. (Cl. ,2.5l)-33.65)

'tenna Systems fnow-abandonedi In: certain-ptypesaof radarsystems andradio altimeters;signalssarezradiated from one antenna and picked. up: by another after reflection: from anaobjec-t-ror. csurface'zwhoseedistance;isrto be determined. It is generally: necessary a to prevent, insofar as ;is .possible; .feed-through *directly from I one .antennato athefother withoutreflection from the object. At the samatimmthe antennas must be "relatively-close together; .inzsome instances-less than aiiwavelengthuapart.

Feed-through:- can :bezsubstantially neutralized, atany .one'efrequency; various--:k-nown methods- However, in frequency-modulation altimetersand the like, theifrequencyq-yaries over-an appreciable range, and neutralization ofrfeedethrough :atzonly one frequency iseineffective;

The principal object-of this-invention is. to provide improved methods-, of and" means" for reducing feed-through between adjacent antennas.

Another. obj GClkiSZtOLPI OVidB; inna system efit-he described type, effective reduction offeedthrough throughout a relatively; wide frequency band rather: thanat 2 only-a single; frequency;

The invention will :be described with reference to the accompanying drawing, wherein:

Figure-111s; amlanwiewoflan antenna structure: embodying therinventiom;

Figure 2 is. .a sectionsof Figure1-1.. along the-line .II-II of 'Figurel and s Figure 31 is -.a-.cross;:.sectional i'view' 01: another embodiment of .ttheinvention.

The :systemrillustrated Sis f the-type :em-ploying series. fed dipoles, as: described and: :claimeckin copending U; S. patent application: Serial No. 619,401, filed September 29, .1945 by 0. 1M. Woodward; Jr; andientitledrAntennas.Systems? now Patent No;.2, 514; 821 dated July'- 11; .1950;- .However, the utility of the present-inventionis xnot limited to this structure;

Referring now moron-particularly to Eiguress 1 and 2, the transmittingantenna l-and;-thea:receiving; antenna: 3.:- are: substantially identical, each comprisingzazpain oft dipolesz-i andfl "and 5- and v1. respectively: ,Iihe:radiator:arms.:ofwthe dipole .5- areaflattwingeshapedisheets; secured: to and F- PP ItBdIbYY mQ" outer conductor: orraacm .axialtransmission-line-9;. A gap ioraslotlil isrprovided: in the outer "conductor of; the. line: 9, between the pointsgof' connection of the two-radiators; Ther d-ipole Tis like the dipoleiand is similarly connectedzacross azgap I3 in the outer ,ponductorof theline 9,, substantially onehalf wavelength from :the gap v-I I The 1 upper "end? of (the line "9 r goes-to" a transmitter; not shown, and: the transmission line is short-circuitedntitslower end.- This short-circuit end is: remote -from' the-point I 3 1 a quarter line wavelength, andtherefore, appears as? an open-circuit at the point l3 so that the dipoles l are theronlyrload seen-by the transmission-line at the point I3; The innerconductor includes no gaps. A panelikezstructure l 5=acts as -a:refleotor forthe antennas-1 and-'3, and supports *thealines iL-and 9 A partition l1- is formed between the antennas {I and'g3.

Rods F 1-9 of" polystyrene or similar insulating materialare secured near theend of eachwing of the dipole-5; extending down (see Fig-urea) toward the bottom of--the pan l5. Aninternally threaded bushing LI in thebottom: of the pan supports-an adjustableisetscrew .23, whose-upper end-engages the lower end-ofthe rod 19. Each wingof each dipole-inhoth antennas l:andz3 'is provided-with similaradjustingemeans; To allow adjustment both above and. below the horizontal plane in Figure 2, the wings: may be -bent downward initially, sothat they act asflatsprings urgingytherods 19 into engagement with" the screws 23.

'I'he'adjustment. and :operation of the systemis vasiollows:

Frequency. modulated energy is-rsupplied to the line-.9 and radiated-by the antennal; Energy picked .up :by theantenna- 3 appears :on the line 9' and is applied to a receiver, :not shown. For

purposes" of adjustment, the assembly as a whole positioned so that: substantially none: of' the radiation from the antenna 1: will strike any nearby reflectingobjects; Any signal appearing on the-line-Bf is thencaused-Lbyfeed-through.

Each wingotthe receiving dipolest' and?! is adjusted-by meansiof'itssetscrew 23' to-the position giving. mini-mumoutputon the line 9 It=will1heapparent that the dipole may be efi'eotively tiltedrwith-respect tothe reflectorpan by running one screwvinaand'theother'out, or may ber benti upgin a broad V shape or down in aninvertedgvf by moving: bothscrews in-the-same direction;

"In,-praotlce-;.it found that both .tiltlng iand --loendins .are:- g nerally: required? for: minimum 3 feed-through. The reason for this is that the antennas I and 3 are so close to each other and to the reflector pan I that they act like loops, as well as dipoles, partly because substantial capacity currents flow from the tips of the radiators to the pan. The radiation from a loop is 90 out of phase with that from a dipole carrying the same current. Thus the coupling between the antennas and 3 comprises two components vectorially at right angles to each other. By tilting the receiving dipoles 5' and 1', pickup 4 adjusted, each wing separately, and in the other case a similar adjustment is made if the discs 30, 3!! may be considered as a portion of the pan reflector being brought closer to or further from the dipole wings.

It will be apparent that the invention affords simple and readily usable means. for reducing feed-through over a relatively wide frequency caused by one of these components can be mini- H mized without greatly affecting the pickup caused by the other component. Similarly,-bending up or down will minimize the other component.

Since the tilting and bending adjustments will interact on each other to some extent, it is necessary to make one adjustment, then the other, and repeat the first, and so on, to achieve mini- -mum' feed-through pickup by the antenna 3. This is followed by a similar sequence of adjust- -ment of the transmitter antenna l to provide minimum field strength at the antenna 1i.

'Although substantially zero couplin can be obtained by critical adjustment of only one of the antennas l and 3, it is desirable to adjust both,

thus superimposing the efiects of the two null conditions. This makes the adjustments less critical, and affords substantial feed-through reduction over a relatively wide frequency band,

Referring now more particularly to Figure 3, an

' embodiment is illustrated only in cross sectional view which may comprise a transmittin antenna l and a receivin antenna 3 which are substantially identical and may be similar to those described'in connection with Figure 1 having dipoles 5, 1 and 5 and I respectively, of which only 5 and 5' are visible in the view of Figure 3. The

connections at the dipoles maybe made in the transmission lines 9 and 9' in a manner similar to that of the embodiment of Figures 1 and 2.

' The same pan-like structure may act as a refiector for the antennas l and 3 and support lines 9 and 9'. A partition I! is formed as before bew tween the antennas I and 3. A sheet l8 of dielectric material may be molded over the open face of the reflector to form a seal against the elements, thus protecting the antenna and permitting the transmission lines 9 and 9 to be pressurized or partially evacuated as desired.

An internally threaded metallic'bushing 2| in the bottom of the pan may support adjustable "metallic setscrews 23 which support on their upper end discs 3D The threaded portion of bushing 2| is' preferably made sufficientl long and close fitting to'provide certain metallic contact between the setscrews and the bushings 2i and thus with the pin 15.

The adjustment and operation of the system of Figure 3 is somewhat similar to that of Figure 1. The assembly as a whole is positioned so that substantially none of the radiation from antenna l strikes any reflecting objects. Any signal appearing on the line 9 is then caused by feedthrough. Each setscrew 23 (and 23' for antenna 3)' is adjusted to the position giving minimum output on the line 9'.

It may be necessary to make the adjustments consecutively and repetitively from setscrew to setscrew.

The operation of both embodiments may be considered as being affected by the change of capacity between the dipole wings 5, 5 and the pan reflector l5. In the one case the distancebetween the antenna wings and the pan itself is.

"each including at least one doublet and a reflector, wherein both electric and magnetic coupling exists between said antennas, the method of minimizing feed-through comprising the stepsof tilting one of said doublets as a whole with respect to said reflector to minimize one of said components of coupling, bending the arms of said doublet with respect to each'other to minimize the other of said components of coupling, and similarly tilting and bending the other of said doublets to further reduce saidrespective components of coupling.

2. In a radio antenna system including a trans- -mitting antenna and a receiving antenna closely adjacent thereto, each of said antennas including at least one doublet, and reflector means for said antennas, the method of minimizing transfer of energy between said antennas, comprising the steps of tilting each of said doublets as a whole to minimize one component of coupling between said antennas, and bending each of said doublets in a broad V-shape to minimize a second component of coupling in quadrature phase with said first-mentioned component.

3. A radio antenna system for reflection-type altimeters and the like,- including a transmitting antenna and a substantially identical receiving antenna in close proximity thereto, each of said antennas comprising a reflector in the form of a shallow pan and a plurality of doublets adjacent and approximately parallel to the bottom of said reflector, each of said doublets including two flat sheet radiator elements; means for adjusting and maintainin adjustment of said elements in respective angular positions with respect to said reflector to minimize feed-through between said antennas, comprising setscrews supported by said reflector adjacent each of said radiator elements and insulating rods connected to said elements and in engagement with said setscrews respectively.

4. In a radio antenna system including apparatus for minimizing transfer of energy be: tween a transmitting antenna and a receiving antenna closely adjacent thereto, each of said antennas including at least one doublet and reflector means for said antennas, the improvement comprising means for tiltin each of said doublets as a whole to minimize one component of said coupling between said antennas, and means for distorting each of said doublets in a broad V- shape to minimize a second component of coupling in quadrature phase with said first-mentioned component.

5.A radio antenna system for reflection-type altimeters and the like, including a transmitting antenna and a substantially identical receiving antenna in close proximity thereto, each'of said antennas comprising a reflector in the form of a shallow pan and a plurality of doublets adjacent reflector, each of said doublets including two ing and maintaining adjustment of said elements in respective angular positions with respect to said reflector to minimize feed-through between said antennas, comprising mechanical actuating means supported by said reflector ad- J'acent each of said radiator elements, and insulating rods connected to said elements and in engagement with said mechanical actuating means respectively. 7

6. In a radio antenna system, apparatus for minimizing transfer of energy between a transmitting antenna and a receiving antenna closely adjacent thereto, each of said antennas including a doublet with two wings and a reflector for the doublet in front of which reflector said doublet is mounted, the improvement comprising sepa rate mechanical means for each antenna wing extending from the reflector toward each wing and independent of the doublet mounting to adjust the efiective distance of the end of each wing of the antenna doublets from the reflector.

'7. In a radio antenna system, apparatus for minimizing transfer of energy between a transmitting antenna and a receiving antenna closely adjacent thereto, each of said antennas inflat sheet radiator elements; means for adjusteluding a doublet having two wings and a reflector for the doublet in front of which said doublet is mounted, the improvement comprising separate mechanical means for each antenna wing extending from the reflector toward each wing and independent of the doublet mounting to adjust the capacitive relationship of each wing of the antenna doublet with the reflector.

8. A radio antenna system for reflection-type altimeters and the like, including a transmitting antenna and a substantially identical receiving antenna in close proximity thereto, each of said antennas comprising a reflector in the form of a shallow pan and a plurality of doublets each with two wings adjacent and approximately parallel to the bottom of said reflector, each of said doublets including two flat sheet radiator elements; means for adjusting and maintaining adjustment of said elements in respective angular positions with respect to said reflector to minimize feed-through between said antennas, comprising mechanical positioning means supported by said reflector adjacent at least some of said radiator elements, and adjustable capacitive means operatively disposed between said mechanical actuating means and said elements.

VERNON D. LANDON.

REFERENCES CITED The following references are of record in the file of'this patent:

UNITED STATES PATENTS Number Name Date 2,093,432 Gordon Sept. 21, 1937 2,155,821 Goldsmith Apr. 25, 1939 2,207,061 Koschmieder July 9, 1940 2,311,435 Gerhard Feb. 16, 1943 2,430,353 Masters Nov. 4, 1947 2,434,893 Alford Jan. 27, 1948 

